This invention relates generally to non-bipolar fuel cells and more specifically to high energy fuel cell stacks that deliver from tens of watts to megawatts of power.
The fundamental components of a prior art non-bipolar fuel cell array are shown in the schematic cross-sectional view of FIG. 1. The basic components are the porous dielectric substrate 1, the electrolyte 6, the fuel electrode 2, the oxidizer electrode 3, the cell breaks 7 and 16, the cell interconnects 12, the external electrical circuit 20, and the electrical load 9. The fuel cell operates with the fuel 10 (such as hydrogen or methanol) dissolving in an electrolyte 6. The dissolved fuel 10 catalytically breaks down into monatomic hydrogen 15 on the catalyzed fuel electrode 2. The monatomic hydrogen 15 travels through the fuel electrode 2, giving up an electron 19 to the electrode 2, and forms a hydrogen ion 17 in the proton conductive electrolyte 5. The electron 19 travels through the cell interconnects 12 to the adjacent cell oxidizer electrode 3, which is formed over conduction electrode 4. The hydrogen ion 17 travels though the conductive electrolyte 5 to the oxidizer electrode 3. At the negative output terminal 22 of the array, electrons 19 flow though the electrical circuit 20 through an electrical load 9 and to the positive terminal of the array 23. The array voltage is determined by the number of cells in the array connected in series. Each of the cells are electrically separated from the adjacent cells by dielectric occupied regions called cell breaks 7 and 16. Adjacent cells are electrically connected by electron conductive vias or cell interconnections 12. At the oxidizer electrode 3 and 4, air 8 is catalytically reacted with the surface of the catalytic electrode 3 to form surface oxygen 13, or oxygen ions 18 in the electrolyte. The oxygen electrode is made of layers of conductive metal films 4 and catalytic electrodes 3. The oxygen ions 18 then receive the electrons from the electrodes 3 and form water 14 (a by-product) at the oxygen electrode 3. On the fuel electrode 2 the fuel is gradually catalytically stripped of it's hydrogen 15 to leave carbon monoxide 24 on the surface of the electrode. The carbon monoxide 24 is oxidized to carbon dioxide 11 by taking the oxygen from water 10 in the fuel or by oxygen 25 which is diffused through the fuel enclosure wall 21. The carbon dioxide 11 by-product diffuses out though the fuel enclosure wall 21 or through the cell break regions 7 and 16. The water 14 by-product diffuses out from the oxygen electrode 3 to the surroundings. This particular example shows the fuel electrode 2 being pore free. This pore free electrode 2 can block fuel diffusion such as methanol 10 while passing monatomic hydrogen 15 to allow the fuel cell to efficiently utilize the methanol fuel. It may also add diatomic hydrogen diffusion impedance while preferentially having a low impedance to monatomic hydrogen, which has been catalyzed. Thus the pore free electrode 2 can also improve the performance of hydrogen fueled fuel cells.
By utilizing liquid methanol and water fuel, this type fuel cell packs more energy in a smaller space than conventional rechargeable batteries. The methanol fuel has effectively 5 to 13 Whr per cubic inch (20% to 50% efficiency) energy density. This is 3 to 9 times the energy density of today's best nickel cadmium batteries, and 40 to 120 times that of standard cellular phone battery packs. Also, these micro-fuel cells are lighter than conventional rechargeable batteries. The methanol fuel has effectively 1200 to 3000 Whr per kg energy per unit mass (20% to 50% efficiency). This is 2 to 5 times the 600 Whr per kg quoted for the latest rechargeable lithium ion batteries (Science News, Mar. 25, 1995). Various patents, such as U.S. Pat. No. 5,631,099, U.S. Pat. No. 5,759,712, U.S. Pat. No. 5,364,711, and U.S. Pat. No. 5,432,023 describe such non-bipolar fuel cells that run on hydrogen, hydrocarbon fuels, and oxygen. However, they do not describe how to assemble these fuel cells into larger parallel fuel cell stacks, which is the primary objective of this patent.
Our earlier U.S. Pat. Nos. 4,673,624 and 5,631,099 describe how to form non-bipolar stacks on insulator substrates. The method of stacking the fuel cells along a common fuel and electrical power connection is also mentioned in our U.S. Pat. No. 5,759,712. The present invention is intended to extend the micro-fuel cell principles set forth in these earlier patents and to show how these fuel cells are configurable into a stack to provide higher power capacity systems with air flow cooling. The present invention also shows how water is used along with air flow cooling to provide a heat and water exchanger.